1. Field of the Invention
The invention relates to electromagnetic relays in general and, in particular, to relays having reduced acoustic noise during pull-in and drop-out. More particularly, the invention relates to an electromagnetic relay having noise dampening means, such as an elastomeric composition, a curable resin or other mechanical dampening composition or material disposed at a juncture between the relay armature and the movable spring in the relay to dampen acoustic noise.
2. Description of the Prior Art
Although reliable and effective from an electrical and mechanical perspective, the noise emitted by a prior art relay, such as that shown in FIGS. 1-3, during mating and unmating can be objectionable when used in certain applications. For example, a relay of this type, as well as comparable relays used for similar applications, can generate an audible noise, when used in proximity to a passenger compartment of an automobile. Extensive steps have been taken to reduce the noise in the passenger compartment, especially in luxury automobiles, and conventional relays used in this environment are considered to be a significant source of unwanted noise.
Relays include a movable contact mounted on a movable spring. The spring holds the movable contact in engagement with a normally closed contact until an increase in coil current generates a magnetic force above a pull-in threshold. An armature, attached to the spring, is attracted to the coil core by the magnetic force. The collision between the armature and the coil core results in an audible sound, which can be magnified due to resonance caused by the cover or other parts of the relay housing. Noise during drop-out occurs when the magnetic force is reduced so that the spring urges the movable contact into engagement again with the normally closed contact. This collision with the normally closed contact can also result in an objectionable noise, even thought the relay has properly performed its switching function.
FIG. 4 is a partial subassembly including an armature 40 and a spring 42 that is used in another prior art relay manufactured and sold by Denso (Malaysia) Sdn Bhd. The part number for this relay is not known. The relay has a die cut plastic or rubber pad 44 positioned between the armature 40 and the spring 42. The specific purpose of this pad 44 is not known. However, manufacture of this relay would appear to be complicated and expensive, requiring a specifically designed armature, and the precise placement of the pad 44 prior to attachment of the armature 40 to the spring 42.
An electromagnetic relay according to this invention includes a magnetic subassembly including a coil surrounding a core. The relay also includes an armature with a contact. When an electric current is applied to the coil, a magnetic force is generated which attracts the armature to the core. A spring biases the armature away from the core so that, when the electric current and magnetic field dissipate, the armature and contact are returned to their original position. Noise dampening means, such as an elastomeric composition or a cured resin composition, for example, is disposed at a juncture between the between the armature and the spring. In one embodiment, the noise dampening means is disposed between the armature and the spring. In another embodiment, the noise dampening means is located at an edge of the armature where it meets the spring. An electromagnetic relay in accordance with this invention exhibits low acoustic noise characteristics upon during pull-in and drop-out.
A resin exhibiting mechanical damping adhering to the spring and to the armature can reduce acoustic noise upon actuation of the relay. A resin or other compositions exhibiting mechanical damping can be deposited on a surface of the relay spring adjacent to an edge of the armature. Deposition of the resin after the armature has been mechanically attached to the spring can simplify manufacture of this low noise relay.